book

Electrical Contacts, 2nd Edition

Name: Electrical Contacts, 2nd Edition
Author: Paul G. Slade
ISBN: 9781351832717

by Paul G. Slade

December 2017

Intermediate to advanced

1311 pages

45h 50m

English

CRC Press

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Cover
Half Title
Title Page
Copyright Page
Table of Contents
Preface to the Second Edition
Preface to the First Edition
Introduction
Editor
Contributors

Part I Contact Interface Conduction
1. Electrical Contact Resistance: Fundamental Principles
1.1 Introduction1.2 Electrical Constriction Resistance1.2.1 Circular a-spots1.2.2 Non-Circular and Ring a-Spots1.2.3 Multiple Contact Spots1.2.4 Effect of the Shape of Contact Asperity on Constriction Resistance1.3 Effect of Surface Films on Constriction and Contact Resistance1.3.1 Electrically Conductive Layers on an Insulated Substrate1.3.1.1 Calculation of Spreading Resistance in a Thin Film1.3.2 Electrically Conducting Layers on a Conducting Substrate1.3.2.1 Electrically Conducting Layers and Thin Contaminant Films1.3.3 Growth of Intermetallic Layers1.3.4 Possible Effect of Electromigration on Intermetallic Growth Rates1.3.5 Electrically Insulating or Weakly Conducting Films1.3.5.1 Growth Rate and Electrical Resistivity of Oxides of Selected Contact Materials1.3.6 Fritting of Electrically Insulating Surface Films1.4 Temperature of an Electrically Heated a-Spot1.4.1 Voltage–Temperature Relation1.4.2 Voltage–Temperature Relation with Temperature-Dependent Electrical Resistivity and Thermal Conductivity1.4.3 The Wiedemann–Franz Law1.4.4 Temperature Distribution in the Vicinity of an a-Spot1.4.5 Deviation of the Voltage–Temperature Relation in an Assymetric Contact1.4.5.1 Case I: Two Metals in Contact1.4.5.2 Case II: A Metal in Contact with a Non-metal1.4.6 Special Considerations on the “Melting” Voltage in Electrical Contacts
1.5 Mechanics of a-Spot Formation
1.5.1 Smooth Interfaces1.5.2 Rough Interfaces1.6 Breakdown of Classical Electrical Contact Theory in Small Contact Spots1.6.1 Electrical Conduction in Small a-Spots1.6.1.1 Contact Resistance1.6.1.2 Joule Heat Flow through a-Spots1.6.2 Observations of Breakdown of Classical Electrical Contact Theory in Aluminum Contacts1.6.2.1 Experimental Data on Aluminum1.6.3 Observations of Breakdown of Classical Electrical Contact Theory in Gold Contacts1.6.4 Observations of Breakdown of Classical Electrical Contact Theory in Tin Contacts1.7 Constriction Resistance at High Frequencies1.7.1 Skin Depth and Constriction Resistance1.7.2 Evaluation of Constriction Resistance at High Frequencies1.7.3 Constriction versus Connection Resistance at High Frequencies1.8 SummaryAcknowledgmentsReferences
2. Introduction to Contact Tarnishing and Corrosion
2.1 Introduction2.2 Corrosion Rates2.3 Corrosive Gases2.4 Types of Corrosion2.4.1 Dry Corrosion2.4.2 Galvanic Corrosion2.4.3 Pore Corrosion2.4.4 Creep Corrosion2.4.5 Metallic Electromigration2.4.6 Stress Corrosion Cracking2.4.7 Contacts under Mineral Oil2.5 Gas Concentrations in the Atmosphere2.6 Measurements2.6.1 Weight Gain Measurement2.6.2 Visual Inspection2.6.3 Cathodic Reduction2.6.4 Scanning Electron Microscopy with Energy-Dispersive X-Ray Spectroscopy (SEM/EDAX)2.6.5 X-Ray Photoelectron Spectroscopy (XPS)2.6.6 Other Techniques2.6.7 Contact Resistance Measurements2.7 Mixed Flow Gas Laboratory Testing2.8 Electronic Connectors2.8.1 Background2.8.2 MFG Test Results2.9 Power Connectors2.10 Other ConsiderationsAcknowledgmentsReferences
3. Gas Corrosion
3.1 Introduction3.1.1 Scope3.1.2 Background3.2 The Field Environments for Electrical Contacts3.2.1 Environmental Variables3.2.2 Corrosion Rates3.2.2.1 Copper and Silver3.2.2.2 Other Metals3.2.2.3 Film Effects3.2.2.4 Shielding Effects3.2.3 Reactivity Distributions3.2.3.1 Severity versus Performance3.2.3.2 Environmental Classes3.2.3.3 Specifications3.2.4 Corrosion Mechanisms3.2.4.1 Silver3.2.4.2 Copper3.2.4.3 Nickel3.2.4.4 Tin3.2.4.5 Porous Gold Coatings3.2.4.6 Pore Corrosion3.2.4.7 Corrosion Product Creep3.3 Laboratory Accelerated Testing3.3.1 Objectives3.3.2 Definition of Acceleration Factor3.3.3 Historical Background3.3.4 Single-Gas Corrosion Effects3.3.4.1 Hydrogen Sulfide3.3.4.2 Sulfur Dioxide (SO2)3.3.4.3 Nitrogen Dioxide (NO2)3.3.4.4 Chlorine3.3.4.5 Mixed-Gas Sulfur Environments3.3.4.6 Humidity3.3.4.7 Temperature3.3.4.8 Gas Flow Effects3.3.5 Mixed-Gas Environments3.3.5.1 Test Systems3.3.5.2 Monitoring Reactivity3.3.6 Test Applications3.3.6.1 Electronic Connectors3.3.6.2 Mated versus Unmated Exposures3.3.6.3 Other Considerations3.4 Lubrication and Inhibition of CorrosionAcknowledgmentReferences
4. Effect of Dust Contamination on Electrical Contacts
4.1 Introduction4.1.1 Background4.1.2 The Importance of the Dust Problem4.1.3 The Complexity of the Problem4.1.4 The Purpose of the Studies4.2 Dusty Environment and Dust Composition4.2.1 The Source of Dust4.2.2 The Collection of the Dust Particles for Testing4.2.3 The Shape of the Dust Particles4.2.4 The Identification of the Inorganic Materials4.2.5 The Organic Materials in Dust4.2.6 The Water Soluble Salts in Dust4.3 The Characteristics of Dust Particles4.3.1 The Electrical Behavior4.3.1.1 Measurement of the Electric Charge4.3.1.2 The Electrostatic Attracting Force on the Particle4.3.2 Mechanical Behavior4.3.2.1 Load Effect4.3.2.2 For Stationary Contacts4.3.2.3 For Sliding Contacts4.3.2.4 The Effect of Lubricants Coated on Contact Surface4.3.2.5 Sliding Contacts on Lubricated and Dusty Contacts4.3.2.6 Fretting (Micro Motion) on Lubricated and Dusty Contacts4.3.3 Chemical Behavior4.3.3.1 Dust Particles Create Pores4.3.3.2 Corrosion Appears as a Result of Dusty Water Solutions4.3.3.3 Indoor Exposure Results4.3.3.4 Construction of the Corrosion Stain4.3.3.5 Fretting Experiments on Dust Corroded Coupon Surfaces…2094.4 Application Conditions in Dusty Environment4.4.1 Explanation of the Special Features4.4.1.1 Covered by Accumulated Small Particles4.4.1.2 Accumulative Particles Caused by Micro Motion4.4.1.3 High and Erratic Contact Resistance4.4.1.4 The Element of Si Causes High Contact Resistance4.4.1.5 Organics Act as Adhesives4.4.1.6 Corrosion Products Trap the Dust Particles4.4.1.7 Difference Between Short Life and Longer Life Contacts4.4.1.8 Large Pieces of “Stepping Stones”4.4.1.9 The Performance of Failed Mobile Phones4.4.2 Other Examples4.5 Theoretical Analysis of Connector Contact Failure due to the Dust4.5.1 Two Micro Worlds in Contact4.5.1.1 Particles Get into the Contact Interface4.5.2 “Preliminary Attachment”4.5.2.1 Adhesive Effect4.5.2.2 Trapping Effect of Corrosion Products4.5.3 Contact Failure Mechanism4.5.3.1 Single Particle and Ideal Model4.5.3.2 Complicated Model – Number of Particles and Morphology of Contact Pairs4.5.4 Micro Movement4.5.4.1 Contact Failure4.6 Future Work4.6.1 Dust Test for Connectors4.6.2 Suggestion of the Dust Test4.6.3 Minimizing the Dust Problem4.6.3.1 Cleaning the SamplesReferences
Part II Nonarcing Contacts
5. Power Connectors
5.1 Introduction5.2 Types of Power Connectors5.2.1 Plug-and-Socket Connectors5.2.2 Wire Connectors5.2.3 Bolted Connectors5.2.4 Insulation Piercing Connectors5.3 Properties of Conductor and Connector Materials5.3.1 Definition of Conductor and Connector Systems5.3.2 Factors Affecting Conductivity5.3.2.1 Effect of Temperature5.3.2.2 Effect of Lattice Imperfections5.3.2.3 Magnetoresistance5.3.2.4 Skin Effect5.3.3 Conductor Materials5.3.3.1 Copper and Copper Alloys5.3.3.2 Aluminum and Its Alloys5.3.4 Materials for Connector Systems5.3.4.1 Pure Metals and Alloys5.3.5 Electroplating and Cladding5.4 Parameters Affecting Performance of Power Connections5.4.1 Factors Affecting Reliability of Power Connections5.4.2 Contact Area5.4.3 Plastic Deformation5.4.4 Elastic Deformation5.4.5 Plated Contacts5.4.6 Oxidation5.4.7 Corrosion5.4.7.1 Atmospheric Corrosion5.4.7.2 Localized Corrosion5.4.7.3 Crevice Corrosion5.4.7.4 Pitting Corrosion5.4.7.5 Pore Corrosion5.4.7.6 Creep Corrosion5.4.8 Dust Corrosion5.4.9 Galvanic Corrosion5.4.10 Thermal Expansion5.4.11 Fretting5.4.11.1 Factors Affecting Fretting5.4.11.2 Mechanisms of Fretting5.4.11.3 Examples of Fretting Damage in Power Connections5.4.11.4 Compression Connectors5.4.11.5 Bus-Stab Contacts
5.4.11.6 Plug-In Connectors
5.4.11.7 Bolted Connections5.4.11.8 Fretting in Aluminum Connections5.4.11.9 Effect of Electrical Current5.4.11.10 Fretting in Coatings (Platings)5.4.11.11 Fretting in Circuit Breaker Contact Materials5.4.12 Intermetallic Compounds5.4.13 Intermetallics in Copper–Tin Systems5.4.13.1 Example of Intermetallics Formation in Power Connections5.4.14 Stress Relaxation and Creep5.4.15 Nature of the Effect of Electric Current5.4.16 Effect of Electric Current on Stress Relaxation5.4.17 Creep5.5 Palliative Measures5.5.1 Contact Area5.5.2 Contact Pressure
5.5.3 Mechanical Contact Device
5.5.4 Disc-Spring (Belleville) Washers5.5.5 Wedge Connectors5.5.6 Automatic Splices5.5.7 Dead-end Connectors5.5.8 Shape-Memory Alloy Connector Devices5.5.9 Coating (Plating)5.5.10 Lubrication—Contact Aid Compounds5.5.11 Bimetallic Inserts5.5.12 Transition Washers5.5.13 Multilam Contact Elements5.5.14 Welded Connections5.5.14.1 Thermite (Exothermic) Welding5.5.14.2 Friction Welding5.5.14.3 Explosion Welding5.5.14.4 Resistance Welding5.5.14.5 Resistance Brazing5.5.15 Connector Design5.5.15.1 Fired Wedge-Connectors5.5.15.2 Stepped Deep Indentation Connectors5.6 Connector Degradation5.6.1 Economical Consequences of Contact Deterioration5.6.2 Power Quality5.7 Prognostic Models5.7.1 Prognostic Model 1 for Contact Remaining Life5.7.2 Prognostic Model 2 for Contact Remaining Life5.7.3 Physical Model5.8 Shape-Memory Alloys (SMA)5.8.1 Origin of Shape-Memory Effect5.8.1.1 One-Way Memory Effect5.8.1.2 Two-Way Memory Effect5.8.2 Applications of SMA in Power Connections5.8.3 Electrical Connections5.8.4 Temperature Indicators5.9 Metal Foam Materials5.9.1 Aluminum Foam Materials5.9.1.1 Electrical and Thermal Properties of Foam Materials5.9.1.2 Power Connection Applications5.9.2 Copper Foam Materials5.9.2.1 Applications of Copper Foam Materials5.9.3 Silver Foam Materials5.10 Installation of Power Connections5.10.1 Examples of Improper Installations5.11 Accelerated Current-Cycling Tests (Standards)5.11.1 Present Current-Cycling TestsReferences
6. Low-Power Commercial, Automotive, and Appliance Connections
6.1 Introduction6.2 Connectors6.2.1 Functional Requirements6.2.2 Types of Connectors6.2.3 Mechanical Considerations6.3 Contact Terminals6.3.1 Contact Physics6.3.2 Terminal Types6.3.3 Other Electrical Contact Parameters6.4 Degradation of Connector Contact6.4.1 Surface Films6.4.2 Fretting Corrosion of Tin–Plated Contacts6.4.3 Examples of Contact Failures6.4.3.1 Automotive Position Sensor Connector6.4.3.2 Fuel Injector Connector6.4.3.3 Glowing Contacts6.4.3.4 Electrolytic Corrosion6.4.3.5 Incompatible Plating and Low Contact Force6.5 Automotive Connector Contacts6.5.1 Vehicle Conditions6.5.2 High Power Connectors for Electric and Hybrid Vehicles6.5.3 Aluminum Wiring Connections6.5.4 Connections for High-Vibration Environment6.6 SummayReferences
7. Tribology of Electronic Connectors: Contact Sliding Wear, Fretting, and Lubrication
7.1 Introduction7.2 Sliding Wear7.2.1 Early Studies7.2.2 Adhesion7.2.2.1 “Wiping” Contaminant from Contact Surfaces7.2.2.2 Mild and Severe7.2.2.3 Prow Formation7.2.2.4 Rider Wear7.2.2.5 Gold Platings: Intrinsic Polymers and Junction Growth7.2.2.6 Electroless Gold Plating7.2.3 Abrasion7.2.4 Brittle Fracture7.2.5 Delamination and Subsurface Wear7.2.6 Effect of Underplate and Substrate7.2.6.1 Hardness7.2.6.2 Roughness7.2.7 Electrodeposited Gold: Relationship of Wear to Underplate Hardness7.2.7.1 Hardener Metal Content7.2.8 Clad Metals7.2.9 Tin and Tin–Lead Alloys7.2.10 Silver
7.3 Fretting
7.3.1 Background7.3.2 Fretting Regimes7.3.3 Static versus Dynamic Contact Resistance7.3.4 Field and Laboratory Testing Methodologies7.3.4.1 Generation of Fretting Displacement7.3.4.2 Determination of Contact Resistance7.3.5 Materials Studies7.3.5.1 Apparatus7.3.5.2 Metals Having Little or No Film-Forming Tendency7.3.5.3 Non-Noble Metals/Fretting Corrosion7.3.5.4 Frictional Polymer-Forming Metals7.3.5.5 Dissimilar Metals on Mating Contacts7.3.6 Wear-Out Phenomena7.3.6.1 Gold-Based Systems7.3.6.2 Palladium-Based Systems7.3.6.3 Tin and Tin–Lead Alloy Systems7.3.6.4 Role of Underplate and Substrate7.3.7 Parametric Studies7.3.7.1 Cycle Rate7.3.7.2 Wipe Distance7.3.7.3 Force7.3.8 Environmental Effects7.3.9 Thermal7.3.10 Effect of Current7.3.11 Surface Finish and Contact Geometry7.3.12 Material Transfer, Wear, Film Formation, and Contact Resistance7.3.12.1 Summary of Physical Processes7.4 Lubrication7.4.1 Introduction7.4.2 Metallic Films7.4.2.1 Principles of Metallic Film Lubrication7.4.2.2 Sliding and Wiping Contacts7.4.2.3 Fretting Contacts7.4.3 Fluid Lubricants7.4.3.1 Background7.4.3.2 Some Fundamental Properties of Lubricants7.4.3.3 Requirements7.4.3.4 Types of Fluid Lubricants: A Sliding Contact Investigation7.4.3.5 Control of Fretting Degradation7.4.4 Grafted and Self-Assembled Lubricant Layers7.4.5 Greases and Solid Lubricants7.4.5.1 Greases7.4.5.2 Solids7.4.6 Lubricant Durability7.4.7 Other ConsiderationsReferences
8. Materials, Coatings, and Platings
8.1 Introduction8.1.1 Scope8.1.2 Requirements of Contact Finishes and Coatings8.1.3 Terminology8.2 Metallic Finishes8.2.1 Wrought Metals8.2.2 Electrodeposits and Electroless Deposits8.2.2.1 Thickness of Platings8.2.2.2 Plating Hardness8.2.2.3 Classification of Platings8.2.3 Contact Finishes Produced by Non-Chemical Methods8.2.4 Metal-in-Elastomer Materials8.2.5 Overview8.3 Properties Related to Porosity8.3.1 Origins of Porosity8.3.2 Tests of Porosity8.3.3 Relationships between Porosity, Thickness of Finish, and Substrate Roughness8.3.4 Effect of Underplatings, Flash Coatings, and Strikes on the Porosity of Electrodeposits8.3.5 Reduction in the Chemical Reactivity of Finishes by the Use of Underplates8.4 Metallurgical and Structural Properties8.4.1 Thermal Diffusion8.4.2 Intermetallics8.4.3 Tin Whiskers8.4.4 Silver Whiskers8.5 Physical and Mechanical Properties8.5.1 Characteristics of Layered Systems8.5.1.1 Hardness8.5.1.2 Contact Resistance8.5.2 TopographyAcknowledgementReferences
Part III The Electric Arc and Switching Device Technology
9. The Arc and Interruption
9.1 Introduction9.2 The Fourth State of Matter9.3 Establishing an Arc9.3.1 Long-Gap Gas Breakdown9.3.2 Vacuum Breakdown and Short-Gap Breakdown9.3.3 The Volt–Current Characteristics of Separated Contacts9.4 The Formation of the Electric Arc9.4.1 The Formation of the Electric Arc during Contact Closing9.4.2 The Formation of the Electric Arc during Contact Opening9.5 The Arc in Air at Atmospheric Pressure9.5.1 The Arc Column9.5.2 The Cathode Region9.5.3 The Anode Region9.5.4 The Minimum Arc Current and the Minimum Arc Voltage9.5.5 Arc Volt–Ampere Characteristics9.6 The Arc in Vacuum9.6.1 The Diffuse Vacuum Arc9.6.2 The Columnar Vacuum Arc9.6.3 The Vacuum Arc in the Presence of a Transverse Magnetic Field9.6.4 The Vacuum Arc in the Presence of an Axial Magnetic Field9.7 Arc Interruption9.7.1 Arc Interruption in Alternating Current Circuits9.7.1.1 Stage 1 - Instantaneous Dielectric Recovery9.7.1.2 Stage 2 - Decay of the Arc Plasma and Dielectric Reignition9.7.1.3 Thermal Reignition9.7.2 Arc Interruption in Direct Current Circuits9.7.3 Vacuum Arc Interruption in Alternating Circuits9.7.4 Arc interruption of Alternating Circuits: Current Limiting9.7.5 Interruption of Low Frequency and High Frequency Power Circuits9.7.6 Interruption of Megahertz and Gigahertz Electronic CircuitsAcknowledgmentsReferences
10. The Consequences of Arcing
10.1 Introduction10.2 Arcing Time10.2.1 Arcing Time in an AC Circuit10.2.2 Arcing Time in a DC Circuit10.2.3 Activation of the Contact10.2.4 Arcing Time in Very Low-Current DC Circuits: Showering Arcs10.3 Arc Erosion of Electrical Contacts10.3.1 Erosion on Make and Erosion on Break10.3.2 The Effect of Arc Current10.3.3 The Effect of Contact Size10.3.4 Determination of Contact Size in AC Operation10.3.5 Erosion of Contacts in Low-Current DC Circuits10.3.6 Erosion of Contacts in Low-Current AC Circuits10.4 Blow-Off Force10.4.1 Butt Contacts10.5 Contact Welding10.5.1 Welding of Closed Contacts10.5.2 Welding during Contact Closure10.5.3 Welding as Contacts Open10.6 Changes in the Contact Surface as a Result of Arcing10.6.1 Silver–Based Contacts10.6.2 Silver–Refractory Metal Contacts10.6.3 Other Ambient Effects on the Arcing Contact Surface: Formation of Silica and Carbon and Contact ActivationAcknowledgmentsReferences
11. Reed Switches
11.1 Principles and Design of the Reed Switch11.1.1 Pull-In Characteristics of a Reed Switch11.1.2 Drop-Out Characteristics of a Reed Switch11.1.3 Magnet Drive Characteristics of a Reed Switch11.1.3.1 X–Y Characteristic H (Horizontal)11.1.3.2 X–Z Characteristic H (Horizontal)11.1.3.3 X–Y Characteristic V (Vertical)11.2 Recommended Contact Plating11.2.1 Materials for Contact Plating11.2.2 Ground Plating11.2.3 Rhodium Plating11.2.4 Ruthenium Plating11.2.5 Other Platings11.2.5.1 Copper Plating11.2.5.2 Tungsten Plating11.2.5.3 Rhenium Plating11.2.5.4 Iridium Plating11.2.5.5 Nitriding the Permalloy (Ni-Fe [48 wt%]) Blade Material11.3 Contact Surface Degradation and Countermeasures11.3.1 Surface Deactivation Treatment11.3.1.1 Life Test of Samples Left for 24 Hours after Sealing11.3.1.2 Life Test of Samples Left for One Week after Sealing11.3.1.3 Life Test of Samples Left for One Month after Sealing11.3.1.4 Life Test of Samples Left for Three Months, Six Months, and One Year after Sealing11.3.2 Prevention of Contact Adhesion11.4 Applications of Reed Switches11.4.1 Reed Relays11.4.2 Applications of Magnetic-Driven Reed SwitchesReferences
12. Low Current and High Frequency Miniature Switches: Microelectromechanical Systems (MEMS), Metal Contact Switches
12.1 Introduction12.1.1 Common MEMS Actuation Methods12.2 Micro-Contact Resistance Modeling12.3 Contact Materials for Performance and Reliability12.4 Failure Modes and Reliability12.5 ConclusionReferences
13. Low Current Switching
13.1 Introduction and Device Classification13.2 Device Types13.2.1 Hand-Operated Switches13.2.1.1 The Rocker Switch Mechanism13.2.1.2 Lever Switches13.2.1.3 Slide Switches13.2.1.4 Rotary Switches13.2.1.5 Push-Button Switches13.2.1.6 Switching Devices Used below 0.5 A13.2.2 Actuated Switches13.2.2.1 Limit Switches13.2.2.2 Thermostatic Controls13.2.2.3 Electro-Mechanical Relay13.3 Design Parameters for Static Switching Contacts13.3.1 Small-Amplitude Sliding Motion13.3.2 Contact Force and Contact Materials13.3.2.1 Contacts at Current Levels below 1 A13.3.2.2 Contacts at Current Levels between 1 and 30 A13.3.2.3 Contact Force13.4 Mechanical Design Parameters13.4.1 Case Study (1): Hand-Operated Rocker-Switch Mechanism13.4.1.1 Moving-Contact Dynamics of a Rocker-Switch Mechanism13.4.1.2 Design Optimization of a Rocker-Switch Mechanism13.4.2 The Opening Characteristics of Switching Devices13.4.2.1 Moving Contact Dynamics at Opening13.4.3 The Make Operation13.4.3.1 Impact Mechanics13.4.3.2 The Coefficient of Restitution13.4.3.3 Impact Mechanics for a Pivoting Mechanism13.4.3.4 The Velocity of Impact13.4.3.5 Bounce Times13.4.3.6 Total Bounce Times13.4.3.7 Impact Times13.4.3.8 Design Parameters for the Reduction of Contact Bounce13.5 The Measurement of Contact Wear and Contact Dynamics13.5.1 The Measurement of Contact Surfaces13.5.2 Three Dimensional (3-D) Surface Measurement Systems13.5.2.1 Contact Systems13.5.2.2 Non-Contact Systems13.5.3 Case Study (2): Example of Volumetric Erosion13.5.4 The Measurement of Arc Motion and Contact Dynamics13.6 Electrical Characteristics of Low-Current Switching Devices at Opening13.6.1 Low-Current DC Arcs13.6.1.1 Arc Voltage Characteristics13.6.1.2 Voltage Steps below 7 A13.6.1.3 Case Study (3): Arc Voltage, Current and Length under Quasi-Static Conditions for Ag/CdO Contacts13.6.1.4 Opening Speed and Arc Length13.6.1.5 Case Study (4): Automotive Systems13.6.2 DC Erosion13.6.2.1 Ag and Ag/MeO Contact Erosion/Deposition13.6.3 Low-Current AC Arcs13.6.3.1 Typical Waveforms and Arc Energy13.6.4 AC Erosion13.6.4.1 Point-on-Wave (POW) Studies Using Ag/CdO Contact Materials13.7 Electrical Characteristics of Low Current Switching Devices at Closure13.7.1 Contact Welding on Make13.7.2 Reducing Contact Bounce13.7.3 Pre-Impact Arcing13.7.4 Influence of Velocity during the First Bounce13.7.4.1 The First Bounce13.7.5 Bounces after the First13.7.6 Summary of Contact Bounce13.8 Summary13.8.1 Switch Design13.8.2 Break Operation13.8.2.1 DC Operation13.8.2.2 AC Operation13.8.3 Make Operation13.8.3.1 Design Parameters13.8.3.2 Reducing Contact Bounce13.8.3.3 Arcing during the Bounce ProcessAcknowledgmentsReferences
14. Medium to High Current Switching: Low Voltage Contactors and Circuit Breakers, and Vacuum Interrupters
14.1 General Aspects of Switching in Air14.1.1 Arc Chutes14.1.2 Magnetic Blast Field14.1.3 Arc Dwell Time on the Contacts14.1.4 Sticking and Back-Commutation of the Arc14.2 Contacts for Switching in Air14.3 Low-Voltage Contactors14.3.1 Principle/Requirements14.3.2 Mechanical Arrangement14.3.3 Quenching Principle and Contact and Arc Chute Design14.3.4 Contact Materials14.3.5 Trends14.3.5.1 Contactors versus Electronics14.3.5.2 Vacuum Contactors14.3.5.3 Hybrid Contactors14.3.5.4 Integration with Electronic Systems14.4 Low-Voltage Circuit-Breakers and Miniature Circuit-Breakers14.4.1 Principle/Requirements14.4.2 General Arrangement14.4.3 Quenching Principle and Design of Arc Chute and Contact System14.4.3.1 Quenching Principles14.4.3.2 Arc Chute and Contact Arrangement14.4.4 Trip System14.4.5 Examples of Miniature Circuit-Breakers14.4.6 Contact Materials14.4.7 Special Requirements for DC Switching14.4.8 Current Limitation by Principles Other than Deion Arc Chutes14.4.8.1 Arcs Squeezed in Narrow Insulating Slots14.4.8.2 Reversible Phase Changes of Liquid or Low-Melting Metal14.4.8.3 Temperature-Dependent Ceramics or Polymers14.4.8.4 Contact Resistance between Powder Grains14.4.8.5 Superconductors14.5 Simulations of Low-Voltage Switching Devices14.5.1 Simulation of Low-Voltage Arcs14.5.1.1 General Principle of Simulation14.5.1.2 Arc Roots on Cathode and Anode14.5.1.3 Radiation14.5.1.4 Interaction between Arc and Electrode or Wall Material (Ablation)14.5.1.5 Plasma Properties14.5.1.6 Simplification by Porous Media14.5.2 Further Simulations of Contact and Switching Device Behavior14.6 Vacuum Interrupters14.6.1 Principle/Applications14.6.2 Design14.6.3 Recovery and the Influence of the Design14.6.4 Contact Materials for Vacuum Interrupters and Their Influence on Switching14.6.4.1 Requirements14.6.4.2 Arc Interruption14.6.4.3 Interruption of High Frequency Transients14.6.4.4 Current Chopping14.6.5 Simulation of Arcs in Vacuum InterruptersReferences
15. Arc Faults and Electrical Safety
15.1 Introduction15.2 Arc Fault Circuit Interrupters (AFCIs)15.3 Arcing Faults15.3.1 Short-Circuit Arcing15.3.2 Series Arcing15.4 Glowing Connections15.5 Arcing Fault Properties15.5.1 Frequency15.5.2 Electrode Materials15.5.3 Arc Fault Current15.5.4 Cable Impedance and Cable Length Effects15.6 Other Types of Arcing Faults15.7 ConclusionsReferences
Part IV Arcing Contact Materials
16. Arcing Contact Materials
16.1 Introduction16.2 Silver Metal Oxides16.2.1 Types16.2.2 Manufacturing Technology16.2.2.1 Internal Oxidation16.2.2.2 Post-Oxidized Internally Oxidized Parts (Process B 1.0)16.2.2.3 One-Sided Internally Oxidized Parts (Process B 2.01)16.2.2.4 Preoxidized Internally Oxidized Parts (Process B.2.02)16.2.2.5 Powder Metallurgical (PM) Silver Metal Oxides (Processes C and D)16.2.3 Electrical Performance Factors16.2.3.1 AC versus DC Testing16.2.3.2 High Current Inrush DC Automotive and AC Loads16.2.3.3 Inductive Loads16.2.3.4 Silver–Tin Oxide Type Materials and Additives16.2.3.5 Material Factor16.2.3.6 Interpreting Material Research, Example from Old Silver Cadmium Oxide Research16.2.4 Material Considerations Based on Electrical Switching Characteristics16.2.4.1 Erosion/Materials Transfer/Welding16.2.5 Transfer/Welding16.2.6 Erosion/Mechanisms/Cracking16.2.7 Erosion/Arc Mobility16.2.8 Interruption Characteristics16.2.9 Contact Resistance16.2.9.1 Summary Metal Oxides16.3 Silver Refractory Metals16.3.1 Manufacturing Technology16.3.1.1 Manufacturing Technology/Press Sinter Repress (Process D 1.0)16.3.2 Material Technology/Extruded Material16.3.2.1 Material Technology/Liquid Phase Sintering (Process D 2.0)16.3.2.2 Material Technology/Press Sinter Infiltration (Process D 3.0)16.3.3 Metallurgical/Metallographic Methods16.3.3.1 Metallurgical/Metallographic Methods/Preparation16.3.3.2 Metallurgical/Metallography/Quantitative Analysis16.3.4 Metallurgical/Structure/Strength and Toughness16.3.5 Electrical Properties (EP)16.3.5.1 EP/Arc Erosion/Microstructure and Properties16.3.5.2 EP/Arc Erosion/Silver Refractory16.3.5.3 EP/Graphite Additions to Silver Tungsten and Silver Tungsten Carbide16.3.5.4 EP/Copper Refractory Metals16.3.5.5 EP/Erosion/Summary16.3.5.6 EP/Composite Refractory Materials/Contact Resistance16.4 Vacuum Interrupter Materials16.5 Tungsten Contacts16.6 Non-Noble Silver Alloys16.6.1 Fine Silver16.6.2 Hard Silver and Silver–Copper Alloys16.7 Silver–Nickel Contact Materials16.8 Silver Alloys and Noble Metals16.8.1 Palladium and Silver–Palladium Alloys16.8.2 Platinum16.9 Silver–Graphite Contact Materials16.10 ConclusionAcknowledgementsReferences
17. Contact Design and Attachment
17.1 Introduction17.1.1 Arc-Induced Contact Stresses and Interface Bond Quality17.2 Staked Contact Assembly Designs17.2.1 Contact Rivets17.2.1.1 Solid Rivets17.2.1.2 Machine-Made Composite Rivets17.2.1.3 Brazed Composite Rivets17.2.1.4 Rivet Staking17.3 Welded Contact Assembly Designs17.3.1 Resistance Welding17.3.1.1 Button Welding17.3.1.2 Wire-Welding17.3.1.3 Contact Tape Welding17.3.2 Special Welding Methods17.3.2.1 Percussion Welding17.3.2.2 Ultrasonic Welding of Contacts17.3.2.3 Friction Welding of Contacts17.4 Brazed Contact Assembly Designs17.4.1 Methods for Brazing Individual Parts17.4.1.1 Torch Brazing17.4.1.2 Induction Brazing17.4.1.3 Direct and Indirect Resistance Brazing17.4.1.4 Furnace Brazing17.4.1.5 Continuous Laminated Strip Brazing, “Toplay”17.4.1.6 Brazed Assembly Quality Control Methods17.5 Clad Metals, Inlay, and Edge Lay17.6 Contact Alloys for Non-Arcing Separable Contacts17.6.1 Gold and Gold Alloys17.6.2 Manufacturing Technology17.6.3 Physical and Chemical Properties17.6.4 Metallurgical Properties17.6.5 Contact Applications and PerformanceAcknowledgmentsReferences
18. Electrical Contact Material Testing Design and Measurement
18.1 Objectives18.2 Device Testing and Model Switch Testing18.2.1 Device Testing18.2.2 Model Switch Testing18.3 Electrical Contact Testing Variables18.3.1 AC versus DC Testing18.3.2 Switching Load Type18.3.3 Opening and Closing Velocity Effects18.3.4 Contact Bounce18.3.5 Contact Carrier Mass and Conductivity18.3.6 Contact Closing Force and Over Travel18.3.7 Enclosed and Open Contact Devices18.3.8 Testing at Different Ambient Temperatures18.3.9 Erosion Measurement18.3.10 Summary Electrical Contact Testing Variables18.4 Electrical Testing Result Types and Measurement Methods18.4.1 Contact Resistance18.4.1.1 Model Testing18.4.1.2 Evaluation and Presentation of Results18.4.2 Contact Bounce Measurement18.4.2.1 Model Testing18.4.2.2 Evaluation18.4.3 Contact Welding Measurement18.4.3.1 Weld Strength Measured18.4.4 Contact Erosion Measurements18.4.4.1 Accelerated and Model Testing18.4.4.2 Extrapolation at Rated Stress18.4.4.3 Increase of the Switching Frequency18.4.4.4 Testing at Increased Electrical Load18.4.4.5 Fixed-Gap Models18.4.4.6 Moving Contact Models18.4.4.7 Evaluation and Presentation of Results18.4.5 AC Arc Reignition Measurement18.4.6 Arc Motion Measurements18.4.6.1 Measurement18.4.6.2 Electronic Optical18.4.6.3 Model Switch Arc Motion Control18.4.6.4 Evaluation and Presentation of Results18.4.7 Arc-Wall Interaction MeasurementsReferences
19. Arc Interactions with Contaminants
19.1 Introduction19.2 Organic Contamination and Activation19.2.1 The Phenomena19.2.2 Sources of Organic Vapors19.2.3 Processes of Contact Activation19.2.4 Activation Effects19.2.5 Activation and Contact Resistance Problems19.2.6 Methods for Detecting Carbon Contamination19.3 Mineral Particulate Contamination of Arcing Contacts19.4 Silicone Contamination of Arcing Contacts19.4.1 Contamination from Silicone Vapors19.4.2 Contamination from Silicone Migration19.4.3 Summary of Silicone Contamination Mechanisms19.5 Lubricants with Refractory Fillers19.6 Oxidation of Contact Materials19.7 Resistance Effects from Long ArcsAcknowledgmentsReferences
Part V Sliding Electrical Contacts
20. Sliding Electrical Contacts (Graphitic Type Lubrication)
20.1 Introduction20.2 Mechanical Aspects20.2.1 Hardness20.2.2 Friction and Wear20.2.3 Tunnel Resistance and Vibration20.3 Chemical Aspects20.3.1 Oxidation20.3.2 Moisture Film20.4 Electrical Effects20.4.1 Constriction Resistance20.4.2 Film Resistance20.4.3 Fundamental Aspects of Commutation20.4.4 Equivalent Commutation Circuit and DC Motor Driving Automotive Fuel Pump20.4.5 Arc Duration and Residual Current20.5 Thermal Effects20.5.1 Steady State20.5.2 Actual Temperature20.5.3 Thermal Mound20.6 Brush Wear20.6.1 Holm’s Wear Equation20.6.2 Flashes and Smutting20.6.3 Polarities and Other Aspects20.7 Brush Materials and Abrasion20.7.1 Electro- and Natural Graphite Brushes20.7.2 Metal Graphite Brush and Others20.8 SummaryReferences
21. Illustrative Modern Brush Applications
21.1 Introduction21.2 Brush Materials21.2.1 Electrographite21.2.2 Carbon-Graphite21.2.3 Graphite21.2.4 Resin-Bonded21.2.5 Metal-Graphite21.2.6 Altitude-Treated Brushes21.3 Brush Applications21.3.1 Minature Motors21.3.2 Fractional Horsepower Motors21.3.2.1 Wound Field/Permanent Magnet-Motor Characteristics21.3.3 Automotive Brush Applications21.3.3.1 Auxiliary Motors21.3.3.2 Alternators21.3.3.3 Starter Motors21.3.4 Industrial Brushes21.3.5 Diesel Electric Locomotive Brushes21.3.6 Aircraft and Space Brushes21.3.7 Brush Design
22. Sliding Contacts for Instrumentation and Control
22.1 Introduction22.2 Sliding Contact—The Micro Perspective22.2.1 Mechanical Aspects22.2.2 Motion Initiation (Pre-Sliding)22.2.3 Friction Forces22.2.4 Motion Continuation22.2.5 Adhesion22.2.6 Adhesive Transfer22.2.7 Plowing, or “Two-Body,” Abrasion22.2.8 Hard Particle, or “Three-Body,” Abrasion22.2.9 Motion Over Time22.3 Electrical Performance22.3.1 Contact Resistance Variation (Noise)22.3.2 Non-Ohmic Noise22.3.3 Non-Linear Noise (Frequency Dependent)22.3.4 Contact Impedance22.3.5 Data Integrity22.4 Micro-Environment of Contact Region22.4.1 Film Forming on the a-Spots22.4.2 Unintentional Contamination22.4.2.1 Particulates22.4.2.2 Contamination or “Air Pollution”22.4.2.3 Organic Off-Gasses22.4.2.4 Friction Polymers22.4.3 Lubrication (Intentional Contamination)22.4.4 Lubrication Modes (Anaerobic and Aerobic)22.4.4.1 Anaerobically Lubricated Contacts22.4.4.2 Aerobically Lubricated Contacts22.4.4.3 Temperature Extremes22.4.4.4 Submerged in Flammable Fuels22.4.4.5 Low-Pressure/Vacuum Operation22.4.4.6 Vapor and Gas Lubrication22.5 Macro Sliding Contact22.5.1 Counterface Configuration22.5.1.1 Flat Surfaces22.5.1.2 Cylindrical Surfaces22.5.1.3 Counterface Contact Shapes22.5.2 Real versus Apparent Area of Contact22.5.3 Brush Configurations22.5.3.1 Cartridge Brush22.5.3.2 Cantilever Composite Brush22.5.3.3 Cantilever Metallic Finger22.5.3.4 Cantilever Wire Brush22.5.3.5 Multifilament or Fiber Brush22.5.3.6 Benefits of Multiple Brushes22.5.4 Forces on the Brush22.6 Materials for Sliding Contacts22.6.1 Materials for Counterfaces22.6.2 Solid Lubricated Composite Materials for Brushes22.6.3 Wire Brush Materials Criteria22.7 Friction and Wear Characteristics22.7.1 Friction22.7.2 Wear22.8 Contact Parameters and Sliding-Contact Assemblies22.8.1 Contact Noise22.8.2 Slip Rings as Transmission Lines22.8.3 Results of Normal Operation22.9 Future22.10 SummaryAcknowledgmentsReferences
23. Metal Fiber Brushes
23.1 Introduction23.1.1 Fiber Brushes for Power23.1.2 Diversification of Applications23.1.3 Outline of Chapter23.2 Sliding Wear of Multi-Fiber Brushes23.2.1 Adhesive Wear23.2.2 Holm-Archard Wear Equation23.2.3 Low Wear Equilibrium23.2.4 High Wear Regime23.2.5 Plastic and Elastic Contact23.2.6 Critical or Transition Brush Pressure23.2.7 Wear of Fiber Brushes23.2.8 Effects of Sliding Speed23.2.9 Effect of Arcing and Bridge Transfer23.3 Surface Films, Friction, and Materials Properties23.3.1 Thin Film Behavior23.3.2 Water Molecules23.3.3 Film Disruption23.3.3 Lubrication23.4 Electrical Contact23.4.1 Dependence of Electrical Resistance on Fiber Brush Construction23.5 Brush Dynamics23.5.1 Speed Effect23.6 Future23.7 SummaryAcknowledgmentsReferences
Part VI Contact Data
24. Useful Electric Contact Information
24.1 Introduction24.2 Notes to the TablesReferences
Author Index
Subject Index

Content preview from Electrical Contacts, 2nd Edition

Introduction

Those who cannot remember the past are condemned to repeat it.

The Life of Reason (Vol. 1), George Santayana

The electrical contact has always been an essential part of the electric circuit. The reliability of the electrical contact has also been an essential, but often ignored, factor—ignored, that is, until it fails. Thus, it sometimes seems as if problems that should have been solved many years ago keep recurring. This perception is, of course, only partially true. In their earliest forms, electric circuits usually carried only a limited range of currents: perhaps up to a few hundred amperes. Since then, this current range has increased considerably. Now electrical contacts of one type or another are found in very high power circuits ...

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Electrical Contacts, 2nd Edition

by Paul G. Slade

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